The present disclosure relates to a method and system for characterizing the steering system of a vehicle and determining symmetry and Ackermann geometry status thereof, and more particularly, to a fault tolerant method and system for determining symmetry and Ackermann geometry of the steering system of a vehicle.
The magnitude of total toe during turns affects both tire wear and vehicle handling. An asymmetrical steering system with different amounts of total toe when steering left or right may indicate faulty components in the vehicle, which can degrade the vehicle handling and cause problems, such as the darting to one side as the vehicle goes over an undulation. Therefore, it is important to know whether the steering system of a vehicle is symmetrical.
For determining proper steering geometry and symmetry of steering systems, automobile manufacturers provide a specification for Toe Out On Turns (TOOT). TOOT is generally measured by requiring technicians to turn the inner wheel in a first direction, say, left, at 20 degrees and measures the toe angle of the outer wheel. The measurement is then compared with a specification value. The same procedure and measurement are repeated for the other direction (in this example, right). As an alternative, total toe is measured and compared with the specification. Asymmetry in the steering system, as indicated by dissimilar TOOT values, is a fairly reliable indicator of damaged or improper steering components, or even chassis damage, including improper repairs after an accident.
Symmetry checks using TOOT measurements have drawbacks. First, TOOT is not always checked during an alignment process. Second, TOOT specification requires taking measurement at 20 degrees, technicians have to precisely position the wheels at the specific angle before toe angle measurements can be taken. Positioning a wheel at a specific angle requires high maneuver precision.
Furthermore, while TOOT measurements are taken at 20 degrees of turn, measurements for various alignment parameters, such as caster and steering axis inclination (SAI, are taken at ten degrees of toe. As a consequence, technicians have to turn the steerable wheels from the straight ahead position through precisely ten degrees to determine caster and steering axis inclination, and then turn another ten degrees to determine TOOT.
Besides, TOOT specifications require taking measurement at 20 degrees of turn. Many aligners do not have the angular range to measure twenty degrees of turn by purely electro-optical means. Although other equipment, such as electronic turnplates, can be used in place of the aligner""s measurement instrument, additional installation is needed, which adds expenses.
Another important characteristic of the steering system of a vehicle is Ackermann geometry. One hundred percent Ackermann geometry is created by using a trapezoidal shaped steering linkage. Ackermann geometry causes all of the vehicle wheels to describe arcs about a common point. Thus, theoretically, eliminating any wheel scrub at low speeds and minimizing tire wear from cornering. Even though most vehicles are designed to have less than one hundred percent Ackermann geometry, significant deviation from one hundred percent Ackermann geometry may be an indication of damaged, non-compliant, or mis-adjusted parts in a vehicle""s steering system, which can cause problems similar to an asymmetric steering system.
FIG. 1 shows a vehicle having true Ackermann geometry. A pair of fixed-direction wheels 10a and 10b are mounted for rotation upon a rear axle 12, and a pair or steerable wheels 14a and 14b are rotatably mounted upon a front axle 16, both pair of wheels being conventionally positioned about the longitudinal axis of the vehicle chassis.
As the wheels are turned, the outer wheel must turn at a lesser angle than the inner wheel to prevent scuffing of the wheels as the vehicle makes a turn. The center lines of the rear and front axles are represented by the axle lines 18 and 20, respectively. The lines 22 and 24 represent the axes of the respective steerable wheels 14a and 14b. A steering system having perfect Ackermann geometry will have an optimum rolling action relative to point O. For purpose of reference, the steerable wheel that is closer to point O during turning is referred to as the inner wheel, while the steerable wheel that is farther than the other steerable wheel relative to point O is referred to as the outer wheel.
Practical limitations of design and requirements for optimizing handling at higher speeds require steering systems designed at other than perfect Ackermann geometry. It has been known that, due to the design of steering systems, perfect Ackermann geometry can be achieved only at one specific turning angle for each turning direction (i.e., left and right). However, significant deviation from Ackermann geometry may indicate defects in the steering system.
Even though pure Ackermann geometry is not practical and generally not desired, the relationship of steering characteristics to theoretically pure Ackermann is an extremely useful tool for the developers of steering systems. Applications for a steering analysis system include vehicle development engineers, racing car development and tuning, collision repair analysis, and heavy truck fleets.
Automobile manufacturers, however, do not publish Ackermann specifications. Without an Ackermann geometry specification, garages have no way to detect and correct errors related to Ackermann geometry.
Therefore, there is a need for effective determination of symmetry of a vehicle""s steering system. There is another need to determine symmetry of a vehicle""s steering system at any toe angle. Still another need exists for determining Ackermann geometry without an Ackermann geometry specification. These and other needs are addressed by the present disclosure.
The disclosure provides a method and system for determining symmetry and Ackermann geometry of a steering system of a vehicle. An advantage of methods and systems according to the disclosure is that, during determining symmetry measurement of a steering system, the steerable wheels can be positioned at any toe angle. Methods and systems according to disclosure are also advantageous in that it allows determination of Ackermann geometry based on a TOOT specification, even without an Ackermann specification. A further advantage of systems and methods according to the disclosure arises from providing an improved alignment procedure that incorporates determination of symmetry of the steering system into other alignment procedures. The present disclosure provides a novel procedure to determine Ackermann geometry of a steering system based on theoretical Ackermann angles. Additionally, a system and method according to the disclosure determines symmetry in a steering system of a vehicle without the need to turn steering wheels through a huge angular range.
A method according to the present disclosure determines symmetry of the steering system of a vehicle of a type having first and second steerable wheels normal to a common axis when the wheels are aligned to a longitudinal axis of the vehicle. The method detects a first measured toe angle of the first steerable wheel when the second steerable wheel is positioned in a first direction at a reference toe angle, such as 10 degrees, and a second measured toe angle of the second steerable wheel when the first steerable wheel is positioned in a second direction at the reference toe angle. The second direction is opposite to the first direction relative to the longitudinal axis of the vehicle. The method determines symmetry of the steering system based on the first measured toe angle and the second measured toe angle.
In one aspect, the method compares determines symmetry of steering system based on the first measured toe angle, the second measured toe angle, and a threshold value. An angle difference between the first measured toe angle and the second measure toe angle is calculated and compared with the threshold value. If the angle difference is larger than the threshold value, the steering system is determined as asymmnetrical.
In one aspect, the first steerable wheel is the right front wheel and the second steerable wheel is the left front wheel. In another aspect, the determination can be made in an inverse way in which the first steerable wheel is the left front wheel and the second steerable wheel is the right front wheel.
A system according to the disclosure determines symmetry of the steering system of a vehicle of a type having first and second steerable wheels normal to a common axis when the wheels are aligned to a longitudinal axis of the vehicle. The system is configured to connect to a measurement device for generating toe angle signals representative of toe angles of the steerable wheels. The system comprises a processor for processing data, a memory, a data storage device for storing data, an input device for inputting data, and a bus coupling to the input device, the memory, the data storage device, and the processor.
The system receives a first signal representative of a first measured toe angle of the first steerable wheel when the second steerable wheel is positioned in a first direction at a reference toe angle, and receives a second signal representative of a second measured toe angle of the second steerable angle when the first steerable wheel is positioned in a second direction at the reference toe angle. The reference toe angle may be any angle preset by the system or set by an operator. The second direction is opposite to the first direction relative to the longitudinal axis of the vehicle. The system determines symmetry of the steering system based on the first measured toe angle and the second measured toe angle. Additionally, the system may determine symmetry of the steering system based on the first measured toe angle, the second measured toe angle, and a threshold value. The threshold value may be determined based on the value of the reference toe angle.
In one aspect, the system determines an angle difference between the first and second measured toe angles. The angle difference is compared with the threshold value. If the angle difference is greater than the threshold value, the steering system is determined as asymmetrical.
Since the reference toe angle can by any angle obtained from any source, such as preset by the system, input by an operator, or obtained from a database, the method and system do not need a TOOT specification to determine symmetry of the steering system.
In another aspect of the disclosure, the determination of symmetry of the steering system is combined into alignment procedures. For example, the detection of the measured angles may be conducted during a caster swing procedure or a Toe Out On Turns procedure. In addition, the reference toe angle may be a predetermined angle, such as 10 degrees, as required in alignment procedures when measuring caster or steering axis inclination. The reference toe angle can be 20 degrees as required by TOOT specification. Thus, symmetry of the steering system can also be determined based on data collected during the existing alignment process without the need of any additional procedures.
Another system according to the present disclosure determines symmetry without the need to position the steering wheel at a specific angle. Rather, the system generates normalized measured angles based on the difference -between the wheel toe angles and a predetermined angle, and determines symmetry of the steering system based on the normalized toe angles.
Another system according to the present disclosure provides a novel approach to determine Ackermann geometry status of a steering system based on a theoretical Ackermann angle. The system is configured to receive a first signal representative of a first toe angle of the first steerable wheel and a second signal representative of a second toe angle of the second steerable wheel when the first steerable wheel is positioned at the first toe angle. A theoretical Ackermann angle is calculated based on a wheelbase value representing the length of the vehicle""s wheelbase, a track width value representing the vehicle""s track width, and the first toe angle. The system determines Ackermann geometry status of the steering system based on the second toe angle and the theoretical Ackermann angle.
The system determines symmetry of the steering system based on the normalized first toe angle and the normalized second toe angle. Alternatively, the system determines symmetry of the steering system based on the normalized first toe angle, the normalized second toe, and a threshold value. For example, an angle difference is calculated between the normalized angles and the angle difference is compared with a threshold value, such as three degrees. If the angle difference is larger than three degrees, the steering system is determined as asymmetrical; otherwise, the steering system is determined as symmetrical.
Thus, technicians can position the wheels at any angle, and, if preferred, near a predetermined angle, such as 20 degrees as required by the TOOT specification. The system calculates the normalized toe angles and determines symmetry accordingly.
Another system according to the present invention provides a novel approach to determine Ackermann geometry status of a steering system based on a theoretical Ackermann angle. The system is configured to receive a first signal representative of a first toe angle of the first steerable wheel and a second signal representative of a second toe angle of the second steerable wheel when the first steerable wheel is positioned at the first toe angle. A theoretical Ackermann angle is calculated based on a wheelbase value representing the length of the vehicle""s wheelbase, a track width value representing the vehicle""s track width, and the first toe angle. The system determines Ackermann geometry status of the steering system based on the second toe angle and the theoretical Ackermann angle.
In one aspect, the system may determine Ackermann geometry status of the steering system based on an Ackermann percentage. The system determines an Ackermann percentage based on the second toe angle and the theoretical Ackermann angle. The Ackermann percentage is then compared with a threshold value. The system determines Ackermann geometry status of the steering system based on a result of the comparison.
In another aspect, the system may have a database that includes values of wheelbase and track width of different vehicle models. Thus, the theoretical Ackermann angle can be calculated by accessing the database without measuring the wheelbase and track width. The values can also be obtained from other sources, such as measured by the system by attaching proper sensors or measurement devices, or the values can be input by an operator by checking a printed reference book, or by measuring manually, such as with a tape measure.
In one aspect of the present disclosure, a troubleshooting process is displayed in response to the steering system being determined as lacking proper Ackermann geometry.
While certain descriptions in the above illustrate the disclosure based on a generic description of first and second steerable wheels, in one aspect of the disclosure, the first steerable wheel may be the right steerable wheel and, the second steerable wheel may be the left steerable wheel. Inversely, the first steerable wheel is the left steerable wheel and the second steerable wheel is the right steerable wheel of the vehicle.
Still other advantages of the present disclosure will become readily apparent from the following detailed description, simply by way of illustration of the disclosure and not limitation. As will be realized, the disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.